diff --git a/masque/test/test_ports2data.py b/masque/test/test_ports2data.py
index 72f6870..8c71437 100644
--- a/masque/test/test_ports2data.py
+++ b/masque/test/test_ports2data.py
@@ -1,10 +1,13 @@
 import numpy
+import pytest
 from numpy.testing import assert_allclose
 
 from ..utils.ports2data import ports_to_data, data_to_ports
 from ..pattern import Pattern
 from ..ports import Port
 from ..library import Library
+from ..error import PortError
+from ..repetition import Grid
 
 
 def test_ports2data_roundtrip() -> None:
@@ -74,3 +77,24 @@ def test_data_to_ports_hierarchical_scaled_ref() -> None:
     assert_allclose(parent.ports["A"].offset, [100, 110], atol=1e-10)
     assert parent.ports["A"].rotation is not None
     assert_allclose(parent.ports["A"].rotation, numpy.pi / 2, atol=1e-10)
+
+
+def test_data_to_ports_hierarchical_repeated_ref_warns_and_keeps_best_effort(
+        caplog: pytest.LogCaptureFixture,
+        ) -> None:
+    lib = Library()
+
+    child = Pattern()
+    layer = (10, 0)
+    child.label(layer=layer, string="A:type1 0", offset=(5, 0))
+    lib["child"] = child
+
+    parent = Pattern()
+    parent.ref("child", repetition=Grid(a_vector=(100, 0), a_count=3))
+
+    caplog.set_level("WARNING")
+    data_to_ports([layer], lib, parent, max_depth=1)
+
+    assert "A" in parent.ports
+    assert_allclose(parent.ports["A"].offset, [5, 0], atol=1e-10)
+    assert any("importing only the base instance ports" in record.message for record in caplog.records)
diff --git a/masque/utils/ports2data.py b/masque/utils/ports2data.py
index c7f42e1..ee8518c 100644
--- a/masque/utils/ports2data.py
+++ b/masque/utils/ports2data.py
@@ -133,6 +133,9 @@ def data_to_ports(
             if not aa.ports:
                 break
 
+            if ref.repetition is not None:
+                logger.warning(f'Pattern {name if name else pattern} has repeated ref to {target!r}; '
+                               'data_to_ports() is importing only the base instance ports')
             aa.apply_ref_transform(ref)
             pattern.check_ports(other_names=aa.ports.keys())
             pattern.ports.update(aa.ports)